Method for guiding a medical instrument through a body

ABSTRACT

Guidance systems for guiding a catheter through tissue within a body are described. In one form, the system is implemented in connection with a catheter which includes a catheter body having a optic fibers extending between a first end and a second end thereof. The guidance system is coupled to the catheter body and includes a first optic fiber, a second optic fiber, and a detecting element. The first optic fiber includes a first end and a second end, and is coupled to the catheter body so that the first optic fiber second end is adjacent the catheter second end. The second optic fiber also includes a first end and a second end, and a reference mirror is positioned adjacent the second optic fiber second end. The first optic fiber first end is communicatively coupled to the detecting element and the second optic fiber first end is communicatively coupled to the detecting element. The detecting element is configured to determine interference between a light beam propagating through the first optic fiber and a light beam propagating through the second optic fiber.

This application is a divisional of U.S. application Ser. No.09/276,379, filed Mar. 25, 1999, now U.S. Pat. No. 6,463,313, which is acontinuation of U.S. application Ser. No. 08/890,631, filed Jul. 9,1997, now U.S. Pat. No. 6,048,349, both of which are hereby incorporatedby reference.

FIELD OF THE INVENTION

This invention relates generally to medical instruments and, moreparticularly, to systems and methods for guiding medical instrumentsthrough a body or a portion of the body, such as a blood vessel.

BACKGROUND OF THE INVENTION

Disease processes, e.g., tumors, inflammation of lymph nodes, and plaquebuild-up in arteries, often afflict the human body. To treat suchdisease, it often is necessary to insert a medical device into the body,and to guide the medical device to the diseased site. Once the medicaldevice is adjacent the diseased site, the medical device typically isused to photoablate or otherwise remove or reduce the diseased tissue.

As one specific example, atherosclerotic plaque is known to build-up onthe walls of arteries in the human body. Such plaque build-up restrictscirculation and often causes cardiovascular problems, especially whenthe build-up occurs in coronary arteries. Accordingly, it is desirableto detect plaque build-up and remove or otherwise reduce such plaquebuild-up.

Known catheters implement laser energy to remove plaque build up onartery walls. One known catheter includes a laser source and a catheterbody. The catheter body has a first end and a second end, or head, andseveral optical fibers extend between the first end and the second end.The laser source is coupled to each of the optical fibers adjacent thecatheter body first end and is configured to transmit laser energysimultaneously through the optical fibers.

To remove arterial plaque, for example, the catheter body is positionedin the artery so that the second end of the catheter body is adjacent aregion of plaque build-up. The laser source is then energized so thatlaser energy travels through each of the optical fibers andsubstantially photoablates the plaque adjacent the second end of thecatheter body. The catheter body is then advanced through the region tophotoablate the plaque in such region.

A guide wire typically is required to properly position the catheter inthe artery. The guide wire is advanced through the artery and region ofplaque build-up so that it forms a path through the artery and plaquebuild-up. The catheter is then guided through the artery using the guidewire.

One known catheter includes ultrasound sensors positioned at its distalend for displaying images of the artery while the catheter is advanced.Known ultrasound sensors are coupled to an outer perimeter of thecatheter and emit sound waves substantially radially from the catheterdistal end toward the artery wall. The sound waves then are reflected bythe surrounding tissue, e.g., the artery wall and plaque, and toward theultrasound sensors. The reflected sound waves are then compared to thetransmitted sound waves to generate an ultrasound image of the tissueradially sounding the distal end.

To advance the catheter, an operator first positions the catheter at afirst location in the artery. Sound waves are then emitted from andreceived by the ultrasound sensors, and an image is then displayedshowing the artery tissue adjacent the circumference of the catheter atsuch first location. The catheter is then advanced to a second locationin the artery, and a second image is displayed showing the artery atsuch location. This process is then continued until the catheter isadvanced through the artery and the plaque-build up.

Utilizing known ultrasound sensors as described above results indisplaying images of the portions of the arterial wall which areradially disposed about the catheter, but does not provide images of thearterial wall or plaque positioned immediately forward the catheter.Particularly, and because of the reflection of the sound waves, thesensors must be aligned within the artery so that the sound wavesprojected toward the artery wall are substantially perpendicular to theartery wall when reflected to the sensors. Sound waves that are notperpendicular to the artery wall may provide inaccurate signals, whichmay result in the display of inaccurate images, which is undesirable.

Inaccurate images may result in improperly guiding the catheter throughthe blood vessel, which is undesirable. Particularly, known cathetersmust be manually inserted and guided through the blood vessel.Typically, a surgeon or other operator utilizes the displayed images toguide the catheter through the vessel and avoid damaging healthy tissue,i.e., the artery wall. If an inaccurate image displays plaque eventhough such tissue actually is an artery wall, it is possible that theoperator may photoablate the artery wall, which is undesirable.

It would be desirable to provide a guidance system which providesimproved image accuracy as compared to known catheters. It also would bedesirable for such guidance system to be substantially easy to implementin connection with medical apparatus other than catheters. It furtherwould be desirable for such guidance system to facilitate automaticadvancement of the catheter through the body.

SUMMARY OF THE INVENTION

These and other objects are attained by a catheter which, in oneembodiment, includes a catheter body and at least one interferometricguidance system. The catheter body includes a bundle of optic fibers,each having a first end and a second end, and the second ends of therespective optic fibers form a substantially rounded catheter head.

Each interferometric guidance system is coupled to the catheter body andincludes a first optic fiber, a second optic fiber, and a detectingelement. The first optic fiber of each guidance system includes a firstend and a second end, and is coupled to the catheter body so that thesecond end is adjacent the catheter head. The second optic fiber of eachguidance system similarly includes a first end and a second end, and areference mirror is positioned adjacent the second optic fiber secondend.

The detecting element of each guidance system is communicatively coupledto both the first optic fiber and the second optic fiber of suchguidance system. Particularly, the first optic fiber first end iscommunicatively coupled to the detecting element and the second opticfiber first end is communicatively coupled to the detecting element. Thedetecting element is configured to determine interference betweensubstantially equal light beams which are emitted from the same sourceand which are split to propagate through the first optic fiber andthrough the second optic fiber. The interference is then utilized todetermine the density and type of tissue adjacent the catheter head, andto guide the catheter head through the tissue.

In operation, the catheter head is inserted at least partially into ablood vessel so that the catheter head and the first optic fiber secondend of each guidance system is positioned in the blood vessel. Thesecond optic fiber of each guidance system is positioned outside theblood vessel. The reference mirror of each guidance system is positioneda desired, or measuring, distance from its respective second optic fibersecond end. The distances between the respective reference mirrors andoptic fiber second ends may either be the same or different.

With respect to each detecting element, a light beam is split into firstand second substantially equal light beams which are then transmittedthrough the first and second optic fibers of each guidance system, fromtheir respective first ends to their respective second ends. The firstlight beam transmitted through the first optic fiber exits from thefirst optic fiber second end, is at least partially reflected by thetissue, re-enters the first optic fiber second end and propagates towardthe first optic fiber first end. Similarly, the second light beamtransmitted through the second optic fiber exits from the second opticfiber second end, is at least partially reflected by the referencemirror, re-enters the second optic fiber second end and propagatestoward the second optic fiber first end.

Each detecting element detects interference between the respectivereflected first light beam and the reflected second light beam andtransmits interference data to a computer. The computer then utilizesthe interference data to determine the density and the type of thetissue to be examined adjacent the catheter head. Particularly, theinterference data is representative of the density and type of tissuelocated at the measuring distance from the second optic fiber secondend, and the computer utilizes such data to generate an image of suchtissue at such location. The computer also utilizes the interferencedata to control subsequent advancement of the catheter through theartery.

The above described guidance systems facilitate obtaining more accurateimages than obtained using ultrasound. In addition, such systems arebelieved to be substantially easy to implement in connection withmedical apparatus other than catheters. Furthermore, such systems arebelieved to facilitate automatic control and advancement of the catheterthrough the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial illustration of a catheter including two guidancesystems in accordance with one embodiment of the present inventioninserted into a blood vessel.

FIG. 2 is a front cross section view of the catheter body shown in FIG.1.

FIG. 3 is a schematic illustration of the catheter control element shownin FIG. 1.

FIG. 4 is a schematic illustration of one of the guidance systems shownin FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a pictorial illustration of a catheter assembly 20 includingtwo guidance systems 22A and 22B in accordance with one embodiment ofthe present invention inserted into a blood vessel 24 of a body.Catheter assembly 20 includes a control element 26 and a catheter body28. Catheter body 28 has a first end 30 and a rounded, or hemispherical,second end, or head, 32, and includes a plurality of optic fibers (notshown in FIG. 1). Catheter body first end 30 is communicatively coupledto control element 26 and catheter body second end 32 is positionedwithin an interior 34 of blood vessel 24 adjacent tissue to be imaged,e.g., plaque 36.

Each guidance system 22A and 22B includes a respective control element40A and 40B, a respective first, or measuring, optic fiber 42A and 42B,and a respective second, or reference, optic fiber 44A and 44B. Firstoptic fibers 42A and 42B include respective first ends 46A and 46B andrespective second ends 48A and 48B, and are coupled to catheter body 28so that second ends 48A and 48B are adjacent catheter head 32 and arepositioned in blood vessel interior 34. Second optic fibers 44A and 44Balso include respective first ends 50A and 50B and respective secondends 52A and 52B. First optic fiber first end 46A and second optic fiberfirst end 50A are communicatively coupled to system control element 40A,and first optic fiber first end 46B and second optic fiber first end 50Bare communicatively coupled to system control element 40B.

First system first optic fiber 42A is configured to emit energy wavessubstantially coaxially with respect to catheter head 32. Second systemfirst optic fiber 42A is configured to emit energy waves substantiallyradially with respect to catheter head 32. Particularly, second end 48Bof optic fiber 42B includes a prism (not shown in FIG. 1) configured toemit an energy beam at an angle with respect to catheter head 32, e.g.,perpendicularly with respect to optic fiber 42A.

Each guidance system control element 40A and 40B includes a respectivediagnostic light beam source 54A and 54B, a respective beam splitter 56Aand 56B, and a respective detecting element 58A and 58B. Beam splitters56A and 56B are communicatively coupled to first optic fiber first ends46A and 46B, respectively. Similarly, beam splitters 56A and 56B arecommunicatively coupled to second optic fiber first ends 50A and 50B,respectively. Beam splitters 56A and 56B also are coupled to respectivediagnostic light beam sources 54A and 54B and detecting elements 58A and58B via optic fibers 64A and 64B, respectively.

Detecting elements 58A and 58B are coupled to an image screen 38 and areconfigured to transmit image data to image screen 38 for displaying animage of the tissue to be imaged. Detecting elements 58A and 58B alsoare configured to transmit control data to catheter control element 26.Particularly, detecting element 58A is configured to determineinterference between a light beam propagating through first optic fiber42A and a light beam propagating through second optic fiber 44A, and togenerate interference data representative of such interference. Forexample, detecting element 58A may include a detector, a demodulator andan analog digitizer which cooperate in a known manner to generate suchinterference data. Such interference data is transmitted to a computer66A, which generates image data for display on image screen 38 andgenerates control data for transmission to catheter control element 26.Similarly, detecting element 58B is configured to determine interferencebetween a light beam propagating through first optic fiber 42B and alight beam propagating through second optic fiber 44B, and to generateinterference data representative of such interference. Such interferencedata is transmitted to a computer 66B, which generates image data fordisplay on image screen 38 and generates control data for transmissionto catheter control element 26.

Referring to FIG. 2, catheter body 28 includes several optic fibers 68extending through a housing, or casing, 70. Second system first opticfiber 42B is coupled to housing 70 so that housing 70 extends betweensuch second system first optic fiber 42B and catheter body optic fibers68. First system first optic fiber 42A extends through and issubstantially centered within housing 70. Alternatively, second systemfirst optic fiber 42B may be positioned within housing 70 and firstsystem optic fiber 42A may be positioned outside housing 70. Of course,both first system optic fibers 42A and 42B may be positioned eitherwithin housing 70 or outside housing 70.

Referring now to FIG. 3, catheter control element 26 includes atherapeutic laser source 72 substantially aligned with catheter bodyoptic fibers 68. Laser source 70 is configured to transmit a therapeuticlaser beam through catheter body optic fibers 68 for photoablatingplaque 36 (FIG. 1), or other tissue.

Referring now to FIG. 4, guidance system 22A further includes areference mirror 74A positioned adjacent second fiber second end 52A.Reference mirror 74A is movable with respect to second fiber second end52A and is controlled, for example, by computer 66A. Similarly, whilenot shown in FIG. 4, guidance system 22B includes a reference mirror 74Bpositioned adjacent second fiber second end 52B. Reference mirror 74B ismovable with respect to second fiber second end 52B and is controlled,for example, by computer 66B.

Prior to inserting catheter assembly 20 into blood vessel 24, eachguidance system 22A and 22B is calibrated. Particularly, referencemirror 74A is positioned a distance D₁ from second fiber second end 52Aand guidance system 22A is calibrated so that interference data obtainedby detecting element 58A is representative of tissue locatedapproximately the same distance D₁ from first optic fiber second end48A. Similarly, reference mirror 74B is positioned a distance D₂ fromsecond fiber second end 52B and guidance system 22B is calibrated sothat interference data obtained by detecting element 58B isrepresentative of tissue located approximately the same distance D₂ fromfirst optic fiber second end 48B.

Referring again to FIG. 1, and after calibrating guidance systems 22Aand 22B, catheter assembly 20 is inserted into blood vessel 24 so thatcatheter head 32 and first optic fiber second ends 48A and 48B arepositioned within blood vessel 24, and second optic fiber second ends52A and 52B are positioned outside blood vessel 24, and outside thebody. First reference mirror 74A, as explained above, is positioneddistance D₁ from second optic fiber second end 52A, and second referencemirror 74B is positioned distance D₂ from second optic fiber second end52B.

Light beam source 54A transmits a diagnostic light beam to beam splitter56A, which splits the light beam into first and second substantiallyequal light beams 76A and 78A, respectively. First light beam 76A isthen transmitted through first optic fiber 42A and second light beam 78Ais transmitted through second optic fiber 44A. First light beam 76Aexits from first optic fiber second end 48A substantially coaxially withrespect to catheter head 32, is at least partially reflected by thetissue, re-enters first optic fiber second end 48A and propagates towardfirst optic fiber first end 46A. Similarly, second light beam 78Atransmitted through second optic fiber 44A exits from second optic fibersecond end 52A, is at least partially reflected by reference mirror 74A,re-enters second optic fiber second end 52A and propagates toward secondoptic fiber first end 50A.

Detecting element 58A detects light interference patterns, e.g.,interferences, between the reflected first light beam 76A and reflectedsecond light beam 78A, and transmits interference data representative ofsuch interferences to computer 66A. Computer 66A utilizes theinterference data to determine the type and depth of the tissue locatedat a distance D₃ from first optic fiber second end 48A. Particularly,computer 66A utilizes the interference data to determine what type oftissue, if any, is located at a distance D₃ from first fiber second end48A, where distance D₃ is substantially the same as distance D₁. Forexample, computer 66A may include a memory, and representativeinterference signals for different types of tissues, e.g., plaque,artery walls, healthy tissue, cancerous tissue, may be stored in suchmemory. Computer 66A compares the interference data received fromdetecting element 58A to such stored representative interference signalsto determine the type of tissue located distance D₃ from first fibersecond end 48A. Distances D₁ and D₃ may, for example, be less than orequal to 1 millimeter, e.g., one quarter of a millimeter. Of course,distances D₁ and D₃ may be larger than 1 millimeter.

If desired, reference mirror 74A may be moved with respect to secondfiber second end 48A to recalibrate guidance system 22A while it ispositioned in a blood vessel 24. Particularly, if detecting element 58Agenerates interference data representative of a loss of signal throughfirst optic fiber 42A, reference mirror 74A may be moved to reestablisha signal at a distance D₄ (not shown in FIG. 1) which is different fromdistance D₁.

Similarly, and in yet another alternative, reference mirror 74A may bemoved with respect to second fiber second end 48A to determine the typeand depth of the tissue located at a varying distances from second fibersecond end 48A. Particularly, reference mirror 74 may be moved between apoint immediately adjacent second fiber second end 48A and a pointdistance D₁ from second fiber second end 48A to determine the type anddepth of the tissue located at each point between such two points.Accordingly, reference mirror 74A may be moved to determine tissue typeat multiple different distances from second fiber second end 48A.

Computer 66A generates image data of such tissue and displays the imageof such tissue on image screen 38. Particularly, computer 66A utilizesthe interference data generated at various points in the tissue togenerate image data representative of a substantially linear imageprofile of the examined tissue. Computer 66A also utilizes theinterference data to generate and transmit control signals to cathetercontrol element 26, as is described in more detail below.

Similarly, light beam source 54B transmits a diagnostic light beam tobeam splitter 56B, which splits the light beam into first and secondsubstantially equal light beams 76B and 78B, respectively. First lightbeam 76B is then transmitted through first optic fiber 42B and secondlight beam 78B is transmitted through second optic fiber 44B. Firstlight beam 76B exits from first optic fiber second end 48B substantiallyradially with respect to catheter head 32, is at least partiallyreflected by the tissue, re-enters first optic fiber second end 48B andpropagates toward first optic fiber first end 46B. Similarly, secondlight beam 78B transmitted through second optic fiber 44B exits fromsecond optic fiber second end 52B, is at least partially reflected byreference mirror 74B, re-enters second optic fiber second end 52B andpropagates toward second optic fiber first end 50B.

Detecting element 58B detects interference between the reflected firstlight beam 76B and reflected second light beam 78B, and transmitsinterference data representative of such interference to computer 66B.Computer 66B utilizes the interference data, as described above, todetermine the type of tissue located a distance D₅ between the tissueand first optic fiber second end 48B, where distance D₅ is substantiallythe same as distance D₂. Computer 66B, utilizing the interference data,generates image data of such tissue, as described above, and displaysthe image on image screen 38. Computer 66B also utilizes theinterference data to generate and transmit control signals to cathetercontrol element 26, as is described in more detail below.

If the tissue located at distance D₃ and D₅ is, for example, plaque 36,then catheter assembly 20 may be utilized to photoablate plaque 36.Particularly, computers 66A and 66B may transmit control signals tocontrol element 26 so that control element 26 energizes laser source 72to transmit a laser beam through catheter body optic fibers 68. Thelaser beam propagates through catheter body optic fibers 68 andphotoablates the plaque 36 in a known manner.

Alternatively, computers 66A and 66B may transmit control signals tocontrol element 26 so that control element 26 energizes laser source 72to transmit a laser beam through only selected catheter body opticfibers 68. For example, if interference data obtained at first systemdetecting element 58A indicates that the tissue in front of catheterhead 32 is plaque 36, and if second system detecting element 58Bindicates that the tissue adjacent second system first optic fiber 42Bis an artery wall, then control element may transmit a laser beam onlythrough optic fibers 68 adjacent first system first optic fiber 42B, andnot through optic fibers 68 adjacent second system first optic fiber42A.

To facilitate determining accurate tissue depth and tissue type duringblood vessel 24 movement, e.g., if blood vessel 24 is located in theheart, where blood vessel 24 may move relative to catheter head 32 evenif catheter head 32 is not advanced through blood vessel 24, guidancesystems 22A and 22B may be configured to determine tissue type anddensity at only periodic intervals. For example, if blood vessel 24 islocated in the heart, and it is not practical to stop the heart, thencomputers 66A and 66B may be configured to sample interference data fromrespective detecting elements 58A and 58B at a same period of time ofthe cardiac cycle. Particularly, computers 66A and 66B may becommunicatively coupled to an EKG and configured to sample interferencedata only at the top of the R wave. Alternatively, computers 66A and 66Bmay be communicatively coupled to an EKG and configured to sampleinterference data only at the middle of the T wave. Of course, computers66A and 66B may be configured to sample interference data at otherperiodic intervals.

The above described catheter and guidance systems facilitate obtaininghigher resolution images than obtained using ultrasound. Such guidancesystems also are believed to be substantially easy to fabricate andutilize in connection with a catheter such as catheter assembly 20.

In an alternative embodiment, the second optic fiber second end prismmay be configured to emit first light beam 76B angularly with respect toan axis of first optic fiber 42B but not perpendicularly with respect tosuch axis. Accordingly, images may be obtained of tissue about acircumference of catheter head 32, rather than merely the tissuepositioned coaxially with catheter head 32 or radially with respect tocatheter head 32.

In addition, and in accordance with yet another embodiment of thepresent invention, a catheter may be utilized in connection withseveral, e.g., five, guidance systems 22. The guidance systems 22 may bepositioned so that respective measuring, or first optic fibers, arepositioned to emit light beams coaxially with respect to the catheterhead, as well as substantially about the entire circumference of thecatheter head.

In still yet another embodiment of the present invention, measuringfibers 42A and 42B are configured to transmit both diagnostic lightbeams from respective diagnostic light beam sources 54A and 54B andtherapeutic laser beams from therapeutic laser source 72. Particularly,measuring fiber 42A is communicatively coupled to both light beam source54A and laser source 72. Similarly, measuring fiber 42B iscommunicatively coupled to both light beam source 54B and laser source72. Laser source 72 and light beam sources 54A and 54B may be configuredto transmits beams having different wave lengths to facilitatesimultaneous transmission of both the therapeutic laser beam anddiagnostic light beams through measuring fibers 42A and 42B.

Guidance systems 22A and 22B may also be implemented in connection withmedical apparatus other than catheters. For example, guidance systems22A and 22B may be coupled to a medical apparatus such as an angioplastyballoon or an atherectomy device. Similarly, guidance systems 22A and22B may be utilized in connection with hollow tubes configured tofacilitate localized treatment. For example, guidance systems 22A and22B may be utilized to position a hollow tube adjacent a region so thatmedicine, radiation, or energy may be transmitted directly to suchregion. Similarly, guidance systems 22A and 22B may be utilized tofacilitate positioning biopsy devices proximate desired sites.

Guidance systems 22A and 22B also facilitate automatic control of theadvancement of catheter assembly 20 through blood vessel 24.Particularly, and in accordance with still yet another embodiment,guidance systems 22A and 22B are coupled to a motor (not shown) which iscoupled to catheter body 28. The motor is configured to advance catheterbody 28 through the body and to receive control signals from respectivecomputers 66A and 66B. If respective computers 66A and 66B transmitcontrol signals indicating that the tissue adjacent catheter head 32 is,for example, plaque, then the motor advances catheter head 32 throughthe plaque. If, however, computers 66A and 66B transmit control signalsindicating that the tissue adjacent catheter head 32 is, for example, anormal artery wall, then the motor stops advancing catheter head 32.

From the preceding description of the present invention, it is evidentthat the objects of the invention are attained. Although the inventionhas been described and illustrated in detail, it is to be clearlyunderstood that the same is intended by way of illustration and exampleonly and is not be taken by way of limitation. For example, while theguidance system was described in connection with a catheter having arounded head, such system may be utilized in connection with a catheterhaving a different shaped, e.g., a spherical, or an angular, head. Inaddition, while the guidance systems included diagnostic light sourcesconfigured to emit a light beam, such light sources may be configured toemit any coherent light beam, such as laser light or polarized light.Furthermore, while each guidance system was described in connection withits own computer, the guidance systems may be coupled to one computer.Accordingly, the spirit and scope of the invention are to be limitedonly by the terms of the claims.

1. A method for guiding a medical instrument having a first end and asecond end through a blood vessel, said method comprising the steps of:coupling at least one guidance system to the medical instrument, theguidance system including a first optic fiber having a first end and asecond end and configured to propagate a sampling light beam, a secondoptic fiber having a first end and a second end and configured topropagate a reference light beam, a reference mirror positioned adjacentthe second optic fiber second end, and a detecting elementcommunicatively coupled to the first ends of the first and second opticfibers; placing the second end of the first optic fiber adjacent thesecond end of the medical instrument; configuring the second end of themedical instrument to direct the sampling light beam substantiallycoaxially with respect to the second end of the medical instrument;inserting the medical instrument at least partially into the bloodvessel; and utilizing the detecting element configured to determineinterference between a light beam propagating through the first opticfiber and a light beam propagating through the second optic fiber toguide the medical instrument through the blood vessel.
 2. A method inaccordance with claim 1 wherein the medical instrument is a catheterhaving a catheter head, and wherein inserting the medical instrument atleast partially into the blood vessel comprising the step of insertingthe catheter head into the blood vessel.
 3. A method in accordance withclaim 1 wherein coupling at least one guidance system to the medicalinstrument comprises the step of coupling at least two guidance systemsto the medical instrument.
 4. A method in accordance with claim 1wherein coupling at least one guidance system to the medical instrumentcomprises the step of coupling five guidance systems to the medicalinstrument.
 5. A method in accordance with claim 1 wherein the medicalinstrument is a catheter.
 6. A method in accordance with claim 1 whereinthe medical instrument is an angioplasty balloon.
 7. A method inaccordance with claim 1 wherein the medical instrument is an atherectomydevice.
 8. A method in accordance with claim 1 wherein the medicalinstrument is a biopsy device.
 9. A method in accordance with claim 1wherein the medical instrument is a hollow tube.
 10. A method inaccordance with claim 1 wherein utilizing the detecting elementconfigured to determine interference comprises the step of generating animage of tissue adjacent the medical instrument.
 11. A method inaccordance with claim 10 wherein said image is a linear profile image ofthe tissue adjacent the medical instrument.
 12. A method in accordancewith claim 10 comprising the step of generating an image of tissuecoaxially aligned with the medical instrument.
 13. A method inaccordance with claim 1 wherein utilizing the detecting elementconfigured to determine interference comprises the step of automaticallycontrolling the medical instrument.
 14. A method in accordance withclaim 1 further comprising the step of utilizing ultrasound for imagingat least portions of the blood vessel.